Audio playback devices become more and more important. Such audio devices usually comprise loudspeakers and/or microphones.
JP 11164396 A discloses a piezoelectric loudspeaker provided by forming a vulcanized rubber at a state of thin film in some parts of a piezoelectric element of the piezoelectric loudspeaker. A metal vibration plate is stuck to the surface of a piezoelectric body of a titanic acid zirconic acid lead sintered body, forming a thin film on the surface by applying a diene rubber made into a heat cross-linked type by adding a sulfur component or a vulcanizable non-diene rubber material or their co-polymer and the thin film is used as the piezoelectric element of the piezoelectric loudspeaker. The heat cross-linked type rubber thin film is also formed on a foaming body. Thus, an edge is formed and a vibration plate-edge integrated type of member capable of supporting the vibration plate is obtained.
EP 0,750443 A discloses a piezoelectric acoustic device comprising a case and a piezoelectric element which is accommodated in the case and has an inner peripheral surface thereof supported by an inner peripheral surface of the case at a middle portion thereof. A plurality of projections are provided on an inner peripheral surface of the case and spaced circumferentially along the inner peripheral surface of the case for supporting the peripheral portion of the piezoelectric element. A gap between the peripheral portion of the piezoelectric element and the inner peripheral surface of the case is closed by an elastic adhesive. A plurality of projections provided on and spaced circumferentially along the inner peripheral surface of the case contact the periphery of the piezoelectric element at the tips thereof, which restricts a radial movement of the piezoelectric element relative to the case.
However, conventional piezoelectric acoustic devices suffer from insufficient performance.